Human bait collections of Aedes albopictus females were made 27 times from May to August, 1990 in Nagasaki, Japan. Seasonal variation was observed in the density, the body size as measured by the wing length and the parous rate of host-seeking females. Early in the observation period, generally the density was lower, the body size was larger and the parous rate was lower. However, when compared in each time period, clear positive correlation was recognized between the body size and the parous rate. It was also found that females with retained mature eggs or with heavily damaged wings had, on average, larger body size, suggesting the longer survival in larger females

Suzuki Akemi

Takagi Masahiro

Tsuda Yoshio

Wada Yoshito

Nagasaki University's Academic Output SITE: NAOSITE

Trop. Med., 35 (3), 91-99, September, 1993 91Seasonal Observation on Some Population Attributes of Aedesalbopictus Females in Nagasaki, Japan, with Emphasis on theRelation between the Body Size and the Survival.Akemi SUZUKI*, Yoshio TSUDA, Masahiro TAKAGI and Yoshito WADADepartment of Medical Entomology, Institute of Tropical Medicine,Nagasaki University, 1 - 12-4, Sakamoto, Nagasaki 852, JapanAbstract: Humanbait collections of Aedes albopictus females were made 27 times fromMay to August, 1990 in Nagasaki, Japan. Seasonal variation was observed in the density,the body size as measured by the wing length and the parous rate of host-seeking females.Early in the observation period, generally the density was lower, the body size was largerand the parous rate was lower. However, when compared in each time period, clear positivecorrelation was recognized between the body size and the parous rate. It was also foundthat females with retained mature eggs or with heavily damaged wings had, on average,larger body size, suggesting the longer survival in larger females.Key words: Aedes albopictus, density, body size, parous rate, survival.INTRODUCTIONSurvival rate of vector insects determines the length of expected life, and therefore isan important parameter affecting the transmission dynamics of vector-borne diseases. Baily(1982) suggested through mathematical studies that vectors with longer expected life have ahigher vectorial capacity. The survival rate is influenced by many physiological andecological factors but much attention has been paid to the relation between the survival rateand the body size of mosquitoes, where in most studies the parous rate is used as asubstitute for the survival rate and the wing length for the body size. Thus, the parous ratewas compared in host-seeking mosquitoes with different wing sizes and/or the wing lengthwas compared in parous and nulliparous mosquitoes.Different results have been reported in the relation between the body size and the pari-ty in many species of mosquitoes. The positive correlation was suggested between the winglength and the parity in Aedes aegypti (Nasci, 1986a), Ae. atlanticus (Nasci, 1986b), Ae. punc-tor (Packer and Corbet, 1989), Ae. sierrensis (Hawley, 1985), Ae. taeniorhynchus (Nasci, 1987),Ae. triseriatus (Haramis, 1983; Nasci, 1988), Ae. vemns (Nasci, 1986b), Culex nigripalpus (Dayet al., 1990), Cx. salinarius (Nasci, 1986b), Psorophom columbiae (Nasci, 1986b), Mansonia* Present address: Institute Adolfo Lutz, Av. Dr. Arnaldo, 355, Sao Paulo-SP 01246, Brazil.Received for Publication September 8, 1993.Contribution No. 2873 from the Institute of Tropical Medicine, Nagasaki University.92dyari (Lounibos et al., 1990), Anopheles crucians (Nasci, 1987), An. dims (Kitthawee et al.,1990, in laboratory) and An. maculatus (Kittayapong et al., 1992). On the other hand, nosignificant correlation was detected in Ae. hendersoni (Walker et al., 1987), Ae. sollicitans(Nasci, 1987), Ae. triseriatus (Landry et al., 1988; Walker et al., 1987), Culiseta melanura(Lorenz et al., 1990), Cs. morsitans (Anderson and Edman, 1990) and An. dims (Kitthawee etal, 1992).The present paper reports the results of seasonal observation on some population at-tributes of Ae. albopictus females in Nagasaki with emphasis on the relation between thebody size and the survival.MATERIAL AND METHODSHumanbait collections of mosquitoes were made 27 times from May to August, 1990in Nagasaki, Japan. Host-seeking female mosquitoes were individually collected by usingglass vials (2cm in diameter and 5cm high) for 10 min in the morning at 9 places in and nearthe campus of Nagasaki University School of Medicine. Collected mosquitoes were im-mediately kept in an ice box to avoid death and wing damage. Identification of female mos-quitoes was carried out in the laboratory under a stereoscopic microscope and Ae. albopictuswere counted. The wing length was measured with an ocular micrometer and the degree ofwing damage was observed and scored according to the Perry's classification (Detinova,1962). Then the mosquitoes were dissected and retained mature eggs in ovaries, if any, werecounted. After these observations, the ovaries were dried on a slide glass and the parity wasdetermined by the tracheolation method (Detinova, 1962).The above population attributes of Ae. albopictus females were examined seasonally anddiscussed. Emphasis was put on the relation between the body size and the survival.RESULTSA total of 1250 host-seeking females of Ae. albopictus female mosquitoes were obtainedby 27 collections from late May to late August, 1990 at 9 places in Nagasaki. The numbersof 2-5 successive collections (2 in late May, 5 in early June and 4 in others) were pooled toshow the seasonal trend.Fig. 1 shows the seasonal change in the mean number per collection. The density offemale mosquitoes was low in late May but increased toward late June, then remained to bestable up to late August. This is the usual seasonal pattern in Nagasaki (Mori and Wada,1978).The mean wing length of the female mosquitoes collected was measured for the bodysize, and its seasonal change is given in Fig. 2. The mosquitoes were large in size early inthe season and small in the late season.Amongthe 1250 Ae. albopictus females in total, the parity could be determined in 1225females. Ovaries of 8 females were infected with Coelomomyces sp. (one in June, two in July93and 5 in August). The seasonal change of the parous rate is shown with the 1225 females inFig. 3. The rate steadily increased from late May to late June, then remained to be ratherconstant.CO0)«50CDmmoos25Fig. 1. Seasonal change in the mean number per collection of Aedesalbopictus host-seeking females, 1990.to ,Mv^ / X§ 80- à"/ X.-P \d) \Cn foà"H 75. ^V701 1 1 1May June July AugustFig. 2. Seasonal change in the mean wing length of Aedes albopictushost-seeking females, 1990. 1 unit of wing length=0.04mm.94The meanwing length of parous and nulliparous female mosquitoes in each time periodis separately given in Table 1. It is noticed that the parous mosquitoes were always largerthan the nulliparous ones during the study period. The difference was significant in the total(t-test, p<0.05) and both in early and late June (p<0.01). The relation between the body size(wing length) and the parous rate in June was further analyzed.The mosquitoes were divided into 5 size groups of equal range (10 units = 0.4mm) ofwing length and the parous rate was calculated for each size group, as shown in Table 2.The parous rate, subjected to the arcsin transform, was positively correlated with the sizegroup of wing length in early June (r=0.987, p<0.01) and in late June (r=0.950, p<0.01).fd ^^^f$ /0.2- /ol 1 1 1May June July AugustFig. 3. Seasonal change in the parous rate of Aedes albopictus host-seeking females, 1990.Table 1. Mean wing length (±sd) of parous and nulliparous host-seekingfemales of Aedes albopictus.Period Elections examined Parous Nulliparous tMay late 2 18 80.25+9.465 79.21±10.977 0.171Jun. early 5 90 84.88+6.681 79.97± 8.889 2.726**late 4 220 8L06±8.651 77.67± 9. 593 2.678**Jul. early 4 208 76.23±7.220 75.02± 8.460 1.112late 4 235 74. 33±7-936 72.47± 8.604 1.724Aug. early 4 207 71.59±8.074 71.51± 7.571 1-078late 4 247 71.97+7.959 70.62± 8.019 1.322Total 27 1225 75-44±8.803 74. 16± 9. 133 2.496*1 unit of wing length=0.04mm.* p<0.05 ** p<0.0195Most host-seeking females had ovaries in the Christopher's stage 1 and 2, but some ofthem were found to retain mature eggs. The frequency distribution of the number of matureeggs retained in ovaries of females is shown in Table 3. Although 1195 females (95.6%) didnot have mature eggs, the remaining ones (4.4%) showed various numbers of retained matureeggs ranging from one to 95. Table 4 gives the comparison of mean wing length in femaleswith and without retained mature eggs in each observation period. The mean wing lengthwas always larger in the females with retained mature eggs than those without, though thedifference was significant (t-test) only in early June, early and late August and total (seeTable 4). Longer survival in females with larger body size was suggested, because excludinga very few autogenous females (Mori, 1979), all the females with retained mature eggs havefed on blood meal at least once and probably oviposited therefore survived for a certainperiod, while a part of the females without mature eggs are certainly newly emerging ones.The frequency distribution of the degree of wing damage in parous and nulliparousmosquitoes is shown in Table 5. The distribution differed significantly (D=0.296, p<0.01,Kolmogorv-Smirnov two-sample test, Sokal and Rohlf, 1981), and the wing of parous mos-quitoes was more heavily damaged than that of nulliparous ones. In Table 6, the averageTable 2. Relation between wing size and parous rate of Aedes albopictushost-seeking females collected in June, 1990. The numeral inparentheses shows the sample size.Size group* Early June** Late June***1 0.00 (3)2 0.ll (9) 0.31 (35)3 0.20 (25) 0.35 (63)4 0.43 (40) 0.45 (91)5 0.56 (16) 0.57 (28)* Group 1, 2, 3, 4 and 5 include mosquitoes with wing length of50-59, 60-69, 70-79, 80-89 and 90-95 units, respectively,where 1 unit=0. 04mm.** r=0.987 (p<0.01)*** r=0.950 (p<0.01)Table 3. Frequency distribution of the number of mature eggs retainedin ovaries of Aedes albopictus host-seeking females.S°eggs Frequency ^f°eggs Frequency g0^ Frequency0 1195 6 1 51 11 24 8 1 64 12 10 13 1 78 13 4 25 1 95 14 5 28 15 2 37 1 Total 1 25096wing size of parous and nulliparous mosquitoes was compared in each class of wing damage,and it was found that parous mosquitoes were larger than nulliparous ones in any wingdamage class, though statistically significant difference was recognized only in the damageclass of score 1 (t=3.917, p<0.001).Table 4. Mean wing length (±sd) of Aedes albopictus host-seekingfemales with and without retained mature eggs.Without mature eggs With mature eggsPeriod tNo.a> Wing length^ No. Wing lengthMay late 17 78.12±10.45 2 87.00±1.41 1.171Jun. early 91 81.09± 8.65 6 90.67±3.56 2.687**late 219 79.09± 9.29 8 83.38±9.04 1.284Jul. early 205 75.56± 7.86 6 79.33+7.23 1.160late 232 73.43± 8.25 8 77.13±3.83 1.247Aug. early 199 71.31± 7.76 9 78.22±6.80 2.625**late 232 70.95± 8.02 16 75.63±6.61 2.280*Total 1195 74.88± 9.02 55 79.85±7.82 4.020***a) No. of females examined. b) 1 unit=0.04mm* p<0.05 ** p<0.01 *** p<0.001Table 5. Frequency distribution of the degree of wing damage in parousand nulliparous host-seeking females of Aedes albopictus.Damage score* Parous Nulliparous Total1 252 492 7442 262 162 4243 48 8 564 1 0 1Total 563 662 1 225* According to the Perry's classification (Detinova, 1962).Wing damage becomes great with increasing score.Table 6. Mean wing length (±sd) in parous and nulliparous host-seekingfemales of Aedes albopictus with different wing damage score.T^ Parous NulliparousDamage 1 tscore") No>b) Wing lengtho No. Wing length1 252 75. 62+8.91 492 74.22±9.04 1. 997*2 262 75. 18±8.70 162 74.09±9. 54 1.2003 48 75.79±8.95 8 71.50±6.39 1.297a) See Table 5. b) No. examined. c) 1 unit=0.04mm.*p<0.0597DISCUSSIONThe female population of Ae. albopidus in early season was characterized by largerbody size and lower parous rate in comparison with smaller body size and higher parous ratein late season (Figs. 2 and 3). However, this does not indicate the negative correlation bet-weenthe body size and the parous rate, because both the parameters are influenced by manyfactors. The body size of mosquitoes is generally larger early in the breeding season inNagasaki due to lower temperatures and relatively larger amounts of larval food. The parousrate is subject to vary by the recruitment rate of adults, the length of a gonotrophic cycleetc., in addition to the real longevity (Tsuda et al, 1991). The reason for seemingly lowerparous rates early in the breeding season can be explained by the fact that the populationwas increasing (Fig. 1). Actually, the positive correlation was clearly shown if we compare ineach observation period the body size in parous and nulliparous females (Table 1) or thebody size and the parous rate (Table 2).Besides the parous rate, the longevity in the field can be indirectly assessed by theretention of mature eggs and the degree of wing damage. The examination of both the twoparameters in relation to wing length implies that larger females of Ae. albopictm survivelonger (Tables 4, 5 and 6). Thus, all evidences reported here with Ae. albopidus suggestlonger survival and therefore greater reproduction potential in larger females.Opposite results were reported in Ae. triseriatus. Haramis (1983) and Nasci (1988)recognized the positive correlation between the body size and the parity, while Walker et al.(1987) and Landry et al. (1988) did not. Although Walker et al. (1987) did not find the effectof body size on survival by mark-release-recapture experiment only with laboratory-rearednormally sized and large mosquitoes, they added that the results may not adequately answerthe question of whether larger mosquitoes live longer than smaller ones when the entirerange of body sizes of natural populations is considered. Landry et al (1988) reported thatthere was-no strong evidence that increased size of females is advantageous to survival, butagain stated that extremely small mosquitoes may have a decreased probability of survival.It was reported that host-seeking females were, on average, larger than emerging onesin Ae. aegypti (Nasci, 1986a) and in Ae. punctor (Packer and Corbet, 1989). In Ae. albopictus,such small females that are not encountered in the field can be produced by rearing larvae inpoor nutritional conditions (Mori, 1979). The correlation between the body size and the sur-vival was detected in An. dims in the laboratory (Kitthawee et al., 1990), but not in the field(Kitthawee et al., 1992). Thus, some small females would not survive long enough to seek ablood meal successfully at least in some mosquito species.The survival rate of mosquitoes is usually estimated by the parous rate, but often thesetwo parameters are not accurately correlated with each other. In Ae. albopictus, for example,the pre-feeding period is longer and multiple feeding is more frequently necessary to developmature eggs in females reared under higher larval density and poorer nutritional condition(Mori, 1979). It is important in the transmission of disease how often infective mosquitoestake blood, therefore not only the parous rate but also the blood-feeding activity would be re-quired to be studied.98REFERENCES1 ) Anderson, R.A. and Edman, J.D. (1990): Body size variation of Culiseta morsitans in relation to vec-tor potential for eastern equine encephalomyelitis virus. J. Amer. Mosq. Control Assoc., 6,723-724.2 ) Bailey, N.T. (1982): The biomathematics of malaria. 210 pp., Griffin, London.3 ) Day, J.F., Ramsey, A.M. and Zhang, J. (1990): Environmentally mediated seasonal variation in mos-quito body size. Environ. Entomol., 19, 469-473.4 ) Detinova, T.S. (1962): Age-grading methods in Diptera of medical importance. 216 pp., WHOMonogr. Ser., 47.5 ) Haramis, L.D. (1983): Increased adult size correlated with parity in Aedes triseriatus. Mosq. News,43,77-79.6 ) Hawley, W.A. (1985): The effect of larval density on adult longevity of a mosquito, Aedes sierrensis:epidemiological consequences. J. Anim. Ecol., 54, 955-964.7 ) Kittayapong, P., Edman, J.D., Harrison, B.A. and Delorme, D.R. (1992): Female body size, parity,and malaria infection of Anopheles maculatus (Diptera: Culicidae) in Peninsular Malaysia. J. Med. En-tomol., 29, 379-383.8 ) Kitthawee, S., Edman, J.D. and Sattabongkot, J. (1990): Evaluation of survival and malaria suscep-tibility among different size classes of laboratory-reared Anopheles dims. Amer. J. Trop. Med. Hyg.,43,328-332.9 ) Kitthawee, S., Edman, J.D. and Upatham, E.S. (1992): Relationship between female Anopheles dims(Diptera: Culicidae) body size and parity in a biting population. J. Med. Entomol., 29, 921-926.10) Landry, S.V., DeFoliart, G.R. and Hogg, D.E. (1988): Adult body size and survivorship in a fieldpopulation of Aedes triseriatus. J. Amer. Mosq. Control Assoc., 4, 121-128.ll) Lorenz, L.H., Scott, T.W., Anderson, R.S., Edman, J.D., Crans, WJ. and Costa, S.D. (1990): Therelationship between size and parity status of field collected Culiseta melanura. J. Amer. Mosq. Con-trol Assoc., 6, 433-440.12) Lounibos, L.P. Larson, V.L. and Morris, C.D. (1990): Parity, fecundity and body size of Mansoniadyari in Florida. J. Amer. Mosq. Control Assoc., 6, 121-126.13) Mori, A. (1979): Effects of larval density and nutrition on some attributes of immature and adultAedes albopidus. Trop. Med. 21, 85-103.14) Mori, A. and Wada, Y. (1978): Seasonal abundanace of Aedes albopidus in Nagasaki. Trop. Med., 20,29-37.15) Nasci, R.S. (1986a): The size of emerging and host-seeking Aedes aegypti and the relation of size toblood-feeding success in the field. J. Amer. Mosq. Control Assoc., 2, 61-62.16) Nasci, R.S. (1986b): Relationship between adult mosquito (Diptera: Culicidae) body size and parity inthe field populations. Environ. Entomol., 15, 874-876.17) Nasci, R.S. (1987): Adult body size and parity in field populations of the mosquitoes Anopheles cru-cians, Aedes taeniorhynchus and Aedes sollicitans. J. Amer. Mosq. Control Assoc., 3, 636-637.18) Nasci, R.S. (1988): Biology of Aedes triseriatus (Diptera: Culicidae) developing in tires in Louisiana.J. Med. Entomol., 25, 402-405.9919) Packer, MJ. and Corbet, P.S. (1989): Size variation and reproductive success of female Aedes punc-tor (Diptera: Culicidae). Ecol. Entomol., 14, 297-309.20) Sokal, R.R. and Rohlf, FJ. (1981): Biometry, 2nd ed. 859 pp., Freeman, San Francisco.21) Tsuda, Y., Takagi, M. and Wada, Y. (1991): Parous rate as a function of basic populationparameters of mosquitoes. Trop. Med., 33, 47-54.22) Walker, E.D., Copeland, R.S., Paulson, S.L. and Munstermann, L.E. (1987): Adult survivorship,population density, and body size in sympatric populations of Aedes triseriatus and Aedes hendersoni(Diptera: Culicidae). J. Med. Entomol., 24, 485-493.

Seasonal Observation on Some Population Attributes of Aedes albopictus Females in Nagasaki, Japan, with Emphasis on the Relation between the Body Size and the Survival.

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Seasonal Observation on Some Population Attributes of Aedes albopictus Females in Nagasaki, Japan, with Emphasis on the Relation between the Body Size and the Survival.

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